The best way to travel through Spain is to keep Google Maps in your phone. You can also download offline maps of some places that you want to travel to so that you can travel without the need of mobile internet or WiFi.
True to its name, the city mapper app shows you an updated map of the various transport options in Istanbul. The app shows you updated fares, routes, and Metro, bus, trams, and ferry routes. It can also calculate taxi fares and show you cycling routes.
Although most people in Greece do speak English, some locals and residents of the islands may have trouble conversing with you. Download Google Translate on your phone to make conversations like asking for directions or just simply wanting to know somebody far more easier.